The field of the present invention relates to imaging using terahertz-frequency radiation. In particular, systems and methods are disclosed for high-contrast, near-real-time acquisition of terahertz images.
A number of systems and methods for generation, detection, or imaging with terahertz-frequency radiation have been disclosed previously. Some of those are disclosed in:                U.S. Pat. No. 5,623,145 entitled “Method and apparatus for terahertz imaging” issued Apr. 22, 1997 to Nuss (Lucent Technologies Inc.);        U.S. Pat. No. 5,710,430 entitled “Method and apparatus for terahertz imaging” issued Jan. 20, 1998 to Nuss (Lucent Technologies Inc.);        U.S. Pat. No. 5,789,750 entitled “Optical system employing terahertz radiation” issued Aug. 4, 1998 to Nuss (Lucent Technologies Inc.);        U.S. Pat. No. 5,894,125 entitled “Near field terahertz imaging” issued Aug. 18, 1997 to Brener et al (Lucent Technologies Inc.);        U.S. Pat. No. 5,939,721 entitled “Systems and methods for processing and analyzing terahertz waveforms” issued Aug. 17, 1999 to Jacobsen et al (Lucent Technologies Inc.);        U.S. Pat. No. 5,952,721 entitled “Electro-optical sensing apparatus and method for characterizing free-space electromagnetic radiation” issued Sep. 14, 1999 to Zhang et al (Rensselaer Polytechnic Institute);        U.S. Pat. No. 6,078,047 entitled “Method and apparatus for terahertz tomographic imaging” issued Jun. 20, 2000 to Mittleman et al (Lucent Technologies Inc.);        U.S. Pat. No. 6,414,473 entitled “electro-optic/magneto-optic measurement of electromagnetic radiation using chirped optical pulse” issued Jul. 2, 2002 to Zhang et al (Rensselaer Polytechnic Institute);        Pub. No. WO 2003/042670 entitled “Method and system for performing three-dimensional terahertz imaging on an object” published May 22, 2003 in the names of Ferguson et al (Rensselaer Polytechnic Institute);        U.S. Pat. No. 7,272,158 entitled “Highly efficient waveguide pulsed THz electromagnetic radiation source and group-matched waveguide THz electromagnetic radiation source” issued Sep. 18, 2007 to Hayes et al;        U.S. Pat. No. 7,339,718 entitled “Generation of terahertz radiation in orientation-patterned semiconductors” issued Mar. 4, 2008 to Vodopyanov et al (Microtech Instruments, Oregon State University, Stanford University);        U.S. Pat. No. 7,349,609 entitled “Terahertz radiation generation and methods therefor” issued Mar. 25, 2008 to Vodopyanov et al;        U.S. Pat. No. 7,929,580 entitled “Inexpensive Terahertz Pulse Wave Generator” issued Apr. 19, 2011 to Moeller (Alcatel-Lucent USA Inc.);        U.S. Pat. No. 8,035,083 entitled “Terahertz tunable sources, spectrometers, and imaging systems” issued Oct. 11, 2011 to Kozlov et al (Microtech Instruments Inc.);        U.S. Pub. No. 2012/0008140 entitled “Terahertz sensing system and method” published Jan. 12, 2012 in the names of Khan et al (Massachusetts Institute of Technology; now U.S. Pat. No. 8,514,393 issued Aug. 20, 2013);        U.S. Pat. No. 8,599,474 entitled “Alignment and optimization of a synchronously pumped optical parametric oscillator for nonlinear optical generation” issued Dec. 3, 2013 to Kozlov et al (Microtech Instruments);        U.S. Pat. No. 8,599,475 entitled “Alignment and optimization of a synchronously pumped optical parametric oscillator for nonlinear optical generation” issued Dec. 3, 2013 to Kozlov et al (Microtech Instruments);        U.S. Pat. No. 8,599,476 entitled “Alignment and optimization of a synchronously pumped optical parametric oscillator for nonlinear optical generation” issued Dec. 3, 2013 to Kozlov et al (Microtech Instruments);        Wu et al; “Two-dimensional electro-optic imaging of THz beams”; Applied Physics Letters Vol. 69 No. 8 p. 1026 (1996);        Jiang et al; “Terahertz imaging via electrooptic effect”; IEEE Transactions on Microwave Theory and Techniques Vol. 47 No. 12 p. 2644 (1999);        Jiang et al; “Improvement of terahertz imaging with a dynamic subtraction technique”; Applied Optics Vol. 39 No. 17 p. 2982 (2000);        Nahata et al; “Two-dimensional imaging of continuous-wave terahertz radiation using electro-optic detection”; Applied Physics Letters Vol. 81 No. 6 p. 963 (2002);        Sutherland et al; Handbook of Nonlinear Optics 2ed (2003); New York: Marcel Dekker;        Yonera et al; “Millisecond THz imaging based on two-dimensional EO sampling using a high speed CMOS camera”; Conference on Lasers and Electro-Optics, Paper No. CMB3 (2004);        Ding et al; “Phase-Matched THz Frequency Upconversion in a GaP Crystal”; Conference on Lasers and Electro-Optics, Paper No. CTuL3 (2006);        Ding et al; “Observation of THz to near-Infrared parametric conversion in ZnGeP2 crystal”; Optics Express Vol. 14 No. 18 p. 8311 (2006);        Hurlbut et al; “Quasi-Phasematched THz Generation in GaAs”; Conference on Lasers and Electro-Optics, Paper No. CTuGG (2006);        Cao et al; “Coherent detection of pulsed narrowband terahertz radiation”; Applied Physics Letters Vol. 88 p. 011101 (2006);        Vodopyanov; “Optical generation of narrow-band terahertz packets in periodically inverted electro-optic crystals: conversion efficiency and optimal laser pulse format”; Optics Express Vol. 14 No. 6 p. 2263 (2006);        Lee et al; “Generation of multicycle terahertz pulses via optical rectification in periodically inverted GaAs structures”; Applied Physics Letters Vol. 89 p. 181104 (2006);        Khan et al; “Optical detection of terahertz radiation by using nonlinear parametric upconversion”; Optics Letters Vol. 32 No. 22 p. 3248 (2007);        Schaar et al; “Intracavity terahertz-wave generation in a synchronously pumped optical parametric oscillator using quasi-phase-matched GaAs”; Optics Letters Vol. 32 No. 10 p. 1284 (2007);        Khan et al; “Optical detection of terahertz using nonlinear parametric upconversion”; Optics Letters Vol. 33 No. 23 p. 2725 (2008);        Vodopyanov et al; “Resonantly-enhanced THz-wave generation via multispectral mixing inside a ring-cavity optical parametric oscillator”; Conference on Lasers and Electro-Optics, Paper No. CTuG1 (2009);        Pedersen et al; “Enhanced 2D-image upconversion using solid-state lasers”; Optics Express Vol. 17 No. 23 p. 20885 (2009).        Hurlbut et al; “THz-wave generation inside a high-finesse ring-cavity OPO pumped by a fiber laser”; Conference on Lasers and Electro-Optics, Paper No. CWF3 (2010);        Tekavec et al; “Efficient high-power tunable terahertz sources based on intracavity difference frequency generation”; Paper No. IRMMW-THz in 36th International Conference on Infrared, Millimeter and Terahertz Waves (2011); and        Tekavec et al; “Terahertz generation from quasi-phase matched gallium arsenide using a type II ring cavity optical parametric oscillator”; Proc. SPIE 8261, Terahertz Technology and Applications V, 82610V; doi:10.1117/12.909529 (2012);        Clerici et al; “CCD-based imaging and 3D space-time mapping of terahertz fields via Kerr frequency conversion”; Optics Letters Vol. 38 No. 11 p. 1899 (Jun. 1, 2013);        Fan et al; “Room temperature terahertz wave imaging at 60 fps by frequency up-conversion in DAST crystal”; Proc. SPIE 8964, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XIII, 89640B (Feb. 20, 2014); doi:10.1117/12.2038685;        Fan et al; “Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate crystal”; Applied Physics Letters, 104, 101106 (2014); doi:10.1063/1.4868134; and        Tekavec et al; “Video Rate 3D THz tomography’: post-deadline paper, Conference on Lasers and Electro-optics (Jun. 8-13, 2014, San Jose, Calif.); incorporated by reference as if fully set forth herein.        